Apparatus, method and software stored on a computer-readable storage medium, for reducing noise in an image

Abstract

An apparatus, method, and software stored on a computer-readable storage medium, for correctly reduce noise included in image data regardless of the characteristics of the image data. The noise reduction apparatus and method employ a determinator for determining whether a target pixel of image data corresponds to a flat portion, an edge portion, or a gradation portion based on a pixel value of the target pixel and pixel values of neighboring pixels of the target pixel; and a noise reduction unit for reducing noise included in the image data based on a result of the determining by the determinator.

1. A noise reduction apparatus comprising:
 a determinator having the capability to assign a flat portion, an edge portion, and a gradation portion to target pixels of image data, the determinator configured to determine whether a target pixel of image data corresponds to the flat portion, the edge portion, or the gradation portion based on a pixel value of the target pixel and pixel values of neighboring pixels of the target pixel; and 
 a noise reduction unit which reduces noise included in the image data based on a result of the determining by the determinator. 
 
     
     
       2. The apparatus of  claim 1 , wherein
 the noise reduction unit comprises a plurality of noise reduction units, 
 at least one of the plurality of noise reduction units is selected based on the result of the determining by the determinator, and 
 the noise included in the image data is reduced by applying the selected at least one noise reduction unit to the target pixel. 
 
     
     
       3. The apparatus of  claim 1 , wherein the noise reduction unit comprises a low pass filter. 
     
     
       4. The noise reduction apparatus of  claim 1 , wherein
 the determinator further has the capability to assign a frequency repetition pattern to the target pixel of image data. 
 
     
     
       5. A noise reduction apparatus comprising:
 a determinator which determines whether a target pixel of image data corresponds to a flat portion, an edge portion, or a gradation portion based on a pixel value of the target pixel and pixel values of neighboring pixels of the target pixel, 
 wherein the determinator calculates at least one characteristic coefficient representing characteristics of the neighboring pixels by using the pixel value of the target pixel and the pixel values of the neighboring pixels, and determines whether the target pixel corresponds to the flat portion, the edge portion, or the gradation portion based on the at least one characteristic coefficient; and 
 a noise reduction unit which reduces noise included in the image data based on a result of the determining by the determinator. 
 
     
     
       6. The apparatus of  claim 5 , wherein
 the at least one characteristic coefficient is obtained by linearly combining absolute values of coefficients representing spatial frequency components of the neighboring pixels, and 
 the determinator determines whether the target pixel corresponds to the flat portion, the edge portion, or the gradation portion based on size relationship of a plurality of characteristic coefficients. 
 
     
     
       7. The noise reduction apparatus of  claim 5 , wherein
 the determinator further determines whether the target pixel of image data corresponds to a frequency repetition pattern based on the pixel value of the target pixel and pixel values of neighboring pixels of the target pixel. 
 
     
     
       8. A noise reduction apparatus comprising:
 a determinator which determines whether a target pixel of image data corresponds to a flat portion, an edge portion, or a gradation portion based on a pixel value of the target pixel and pixel values of neighboring pixels of the target pixel; and 
 a noise reduction unit which reduces noise included in the image data based on a result of the determining by the determinator, 
 wherein the noise reduction unit to be applied when it is determined that the target pixel corresponds to the gradation portion has a noise reduction strength greater than that of the noise reduction unit to be applied to when it is determined that the target pixel corresponds to the flat portion. 
 
     
     
       9. The noise reduction apparatus of  claim 8 , wherein
 the determinator further determines whether the target pixel of image data corresponds to a frequency repetition pattern based on the pixel value of the target pixel and pixel values of neighboring pixels of the target pixel. 
 
     
     
       10. A noise reduction method comprising:
 calculating at least one characteristic coefficient representing characteristics of neighboring pixels of a target pixel of image data by using a pixel value of the target pixel and pixel values of the neighboring pixels; 
 determining whether the target pixel corresponds to a flat portion, an edge portion, or a gradation portion based on the at least one characteristic coefficient; and 
 reducing noise included in the image data based on a result of the determining. 
 
     
     
       11. The method of  claim 10 , wherein the calculating calculates said at least one characteristic coefficient representing characteristics of the neighboring pixels by using the pixel value of the target pixel and the pixel values of the neighboring pixels, and determines whether the target pixel corresponds to the flat portion, the edge portion, or the gradation portion based on the at least one characteristic coefficient. 
     
     
       12. The method of  claim 11 , wherein
 the at least one characteristic coefficient is obtained by linearly combining absolute values of coefficients representing spatial frequency components of the neighboring pixels, and 
 the determining determines whether the target pixel corresponds to the flat portion, the edge portion, or the gradation portion based on size relationship of a plurality of characteristic coefficients. 
 
     
     
       13. The method of  claim 10 , wherein
 the noise reducing includes selecting at least one of a plurality of noise reduction units based on the result of the determining, and reducing the noise included in the image data by applying the selected at least one noise reduction unit to the target pixel. 
 
     
     
       14. The method of  claim 10 , wherein the noise reduction to be applied during the noise reducing, when it is determined that the target pixel corresponds to the gradation portion, has a noise reduction strength greater than that of the noise reduction to be applied to when it is determined that the target pixel corresponds to the flat portion. 
     
     
       15. The method of  claim 10 , wherein the noise reducing comprises operating a low pass filter to filter the noise. 
     
     
       16. A non-transitory computer-readable storage medium having recorded thereon a program for executing a noise reduction method, the method comprising:
 calculating at least one characteristic coefficient representing characteristics of neighboring pixels of a target pixel of image data by using a pixel value of the target pixel and pixel values of the neighboring pixels; 
 determining whether the target pixel corresponds to a flat portion, an edge portion, or a gradation portion based on the at least one characteristic coefficient; and 
 reducing noise included in the image data based on a result of the determining. 
 
     
     
       17. The non-transitory computer-readable storage medium of  claim 16 , wherein the calculating calculates said at least one characteristic coefficient representing characteristics of the neighboring pixels by using the pixel value of the target pixel and the pixel values of the neighboring pixels, and determines whether the target pixel corresponds to the flat portion, the edge portion, or the gradation portion based on the at least one characteristic coefficient. 
     
     
       18. The non-transitory computer-readable storage medium of  claim 17 , wherein
 the at least one characterisitic coefficient is obtained by linearly combining absolute values of coeficients representing spatial frequency components of the neighboring pixels, and 
 the determining determines whether the target pixel corresponds to the flat portion, the edge portion, or the gradation portion based on size relationship of a plurality of characteristic coefficients. 
 
     
     
       19. The non-transitory computer-readable storage medium of  claim 16 , wherein the noise reducing includes selecting at least one of a plurality of noise reduction units based on the result of the determining, and reducing the noise included in the image data by applying the selected at least one noise reduction unit to the target pixel. 
     
     
       20. The non-transitory computer-readable storage medium of  claim 16 , wherein the noise reduction to be applied during the noise reducing, when it is determined that the target pixel corresponds to the gradation portion, has a noise reduction strength greater than that of the noise reduction to be applied to when it is determined that the target pixel corresponds to the flat portion. 
     
     
       21. The non-transitory computer-readable storage medium of  claim 16 , wherein the noise reducing comprises operating a low pass filter to filter the noise. 
     
     
       22. The method of  claim 10 , further comprising:
 determining whether the target pixel of image data corresponds to a frequency repetition pattern based on the at least one characteristic coefficient.